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1. Field of the Invention
The present invention relates to a system and method for the communication of digital information. More specifically, the present invention relate s to a modulation and demodulation system and method for the communication of bits of digital information.
2. Background Art
Technologies that rely upon the high-speed transfer of digital information are growing rapidly. The growth of these technologies has been accompanied by the concomitant need for faster digital transmission rates. For example, development in the areas of digital networking and telecommunications have created a desire for increased digital transmission rates to accommodate the rapid transfer of increasingly larger amounts of digital information.
Wireless technologies in particular may require the high-speed transmission of digital data. For example, there is a considerable need for devices that provide for wireless high-speed digital communication to connect different clusters of networks together. To satisfy this need, some companies have manufactured high speed point-to-point transceivers using advanced digital modulation techniques such as 16- or 64-Quadrature Amplitude Modulation (QAM), and M-ary Phase-Shift Keying (PSK).
Current digital modulation techniques are limited, however, in that an increase in the transmission bit rate often results in a decrease in the overall reliability of transmitted data and/or a required increase in the power of the transmitted signal.
For example, conventional Binary PSK (BPSK) systems transmit one bit per pulse. In one embodiment of a conventional BPSK system, a pulse phase of 0xc2x0 will correspond to a bit value of 0 and a pulse phase of 180xc2x0 will correspond to a bit value of 1. The customary technique for doubling the bit rate of such a BPSK system is to increase the number of phase shifts available for the pulses from two (0xc2x0 and 180xc2x0) to four (0xc2x0, 90xc2x0, 180xc2x0and 270xc2x0), thus permitting two bits to be transferred per pulse as opposed to a single bit. However, it has been observed that increasing the number of available phase shifts (and hence the number of bits that may be transferred per pulse) has resulted in a higher probability of bit errors upon reception of a transmitted signal. To avoid this inherent decrease in reliability, the power of the transmitted signal must be increased, which has the undesired effect of increasing the size, complexity and cost of digital communication components.
A similar limitation has been observed in conventional QAM systems. A conventional QAM modulation technique combines phase and amplitude modulation to transfer two bits per pulse time, Tb. To increase the transmission rate to four bits per pulse time Tb, 16-QAM can be used. In 16-QAM, four amplitude levels and two phase shifts are used, resulting in 16 different phase/amplitude combinations for encoding four bits of data. When 64-QAM is used, 6 bits may be represented per pulse by increasing the number of amplitude levels from four to eight. While increasing the number of amplitude levels in QAM modulation permits an increased bit rate, the increase also results in a higher probability of bit errors upon reception. To maintain a consistent level of reliability, more transmission power is required at higher bit rates. If the power level is not increased, then the probability of bit errors will be higher.
What is needed, then, is a novel modulation and demodulation system and method for communicating digital information that provides for an increased bit rate without a corresponding loss in reliability of the transmitted information, and without a need for increased transmission power.
The present invention is directed to a communication system and method for increasing the transfer rate of digital information. According to the present invention, a method for transmitting digital information is provided that includes receiving one or more bits, modulating the one or more bits onto a carrier signal to generate a first transmission signal during a first part of a pulse time TB , receiving an additional bit, determining whether the additional bit is a first value or a second value, transmitting the first transmission signal during a second part of the pulse time TB if the additional bit is the first value, and transmitting a second transmission signal during the second part of the pulse time TB if the additional bit is a second value.
A method for receiving digital information in accordance with the present invention is also provided that includes receiving a transmission signal, demodulating the transmission signal during a first part of a pulse time TB to determine a value for one or more received bits, accumulating a voltage from the transmission signal during a second part of the pulse time TB to generate an accumulated voltage, measuring the accumulated voltage, assigning a first value to an additional received bit if the accumulated voltage is within a first voltage range, and assigning a second value to the additional received bit if the accumulated voltage is within a second voltage range.
A transmitter for transmitting digital information in accordance with the present invention comprises a modulator for receiving one or more bits and modulating the one or more bits onto a carrier signal to generate a first transmission signal, control logic for receiving an additional bit and determining whether the additional bit is a first value or a second value, a transmitter antenna, and a switch, wherein the switch is controlled by the control logic to couple the first transmission signal to the transmitter antenna during a first part of a pulse time TB, and wherein the switch is controlled by the control logic to couple the first transmission signal to the transmitter antenna during a second part of the pulse time TB when the additional bit is the first value and to couple a second transmission signal to the transmitter antenna during the second part of the pulse time TB when the additional bit is the second value.
A receiver for receiving digital information in accordance with the present invention comprises a receiver antenna for receiving a transmission signal, a demodulator for demodulating the transmission signal during a first part of a pulse time TB to determine a value for one or more received bits, an accumulator for accumulating a voltage from the transmission signal during a second part of the pulse time TB to generate an accumulated voltage, and a decision circuit for measuring the accumulated voltage, wherein the decision circuit assigns a first value to an additional received bit if the accumulated voltage is within a first voltage range and assigns a second value to the additional received bit if the accumulated voltage is within a second voltage range.
The invention is advantageous in that it provides an increased transfer rate of digital information without impairing the reliability of the transmission.
The invention is also advantageous in that it provides an increased transfer rate of digital information while also improving the reliability of the transmission.
A further advantage of the invention is that it provides an increased transfer rate of digital information while requiring less power than conventional digital communication systems and methods that provide comparable transfer rates.
Another benefit of the invention is that it may be implemented in conjunction with any existing digital modulation and demodulation technique to improve transfer rate and transmission reliability.
Yet another benefit of the invention is that it may be implemented in conjunction with M-ary PSK digital modulation and demodulation techniques to improve transfer rate and transmission reliability.
A further advantage of the invention is that it may be implemented in conjunction with QAM, 16-QAM and 64-QAM digital modulation and demodulation techniques to improve transfer rate and transmission reliability.
A further benefit of the invention is that it provides a low-cost solution for improving the transfer rate of a digital communication system.
Another benefit of the invention is that it can be easily implemented in conjunction with existing digital communication components to improve system performance.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the system and method particularly pointed out in the written description and claims hereof as well as the appended drawings.